Chair backrest detail



FIG. 1 is a perspective view of a chair backrest detail according to our new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a left side view thereof; and,

FIG. 4 is a right side view thereof.

Features shown in dashed lines form no part of the claimed design. 

The ornamental design for a chair backrest detail, as shown and described. 